The invention relates to a device for stabilizing the flow in the exhaust line of an internal combustion engine, in particular, at the exhaust side exit of an exhaust turbocharger downstream of an internal combustion engine, comprising a guide baffle including a plurality of web plates extending in the direction of flow transversely to the exhaust pipe.
In the design of exhaust gas turbochargers two negative effects can frequently be observed. On catalysts close to the engine a poor flow distribution along the end face of the catalyst body occurs, having a particularly negative effect if the engine runs under partial load, because in that situation the exhaust flow is subjected to strong spin effects. This results in a decreased exhaust purification effect of the catalyst.
Particularly in the case of exhaust gas turbochargers of modern design with adjustable guide blades a particularly unpleasant noise formation comparable with a howling noise is experienced in the exhaust train at certain rates of revolution under partial load, which is transmitted all the way to the outlet noise. Although this noise can be muffled in the silencer device, this can be achieved only at substantially increased cost. In certain particularly constricted installation situations an additional problem arises in that for such silencing requirements the additionally needed silencer volume cannot be accommodated below the vehicle floor.
U.S. Pat. No. 4,529,356 A discloses a device of the type set out in the introduction. In that case the exhaust turbocharger of a turbocharged internal combustion engine is followed downstream by a slightly conically diverging casing, a guide baffle comprising eight radially extending web plates being provided in the region of maximum flow cross-section.
It is an object of the present invention to provide a device of the type set out in the introduction which can be manufactured at minimum cost, the device preferably requiring no additional installation space for flow stabilization and wherein the aforesaid two disadvantages associated with the provision of an exhaust turbocharger are substantially avoided.
According to the invention, this object is attained by a device in accordance with claim 1. The device according to the invention for flow stabilization is accordingly characterized in that the guide baffle is manufactured by squeezing or pressure-deforming a sheet metal ring. The sheet metal ring may in this context more particularly be formed by a thin-walled pipe section. The deformation of the sheet metal ring proceeds preferably in such a manner that the web plates do not enter into mutual contact but at the most approximate each other to within a narrow gap width.
With such a simple device which preferably is installed directly onto the outlet of the exhaust turbocharger, it was surprisingly possible not only to attain the desired even flow at the inlet into the catalyst, but also to bring about the desired silencing effect. Thus in the measured problematic frequency range a silencing effect of 12 dB was attained, which, in total, i.e. when measured over all frequencies amounts to an actual drop of 8 dB. If one were instead to operate with a conventional stabilizer, composed e.g. of a plurality of small tubes, the same effect would only be attainable at higher cost and increased length of the structure; without such a stabilizer one would require a straight pipe length corresponding approximately in length to ten times the pipe diameter of the exhaust pipe.
By way of contrast according to the solution proposed by the invention, the web plates only extend over a short length of the exhaust pipe, an axial length of the web plates being, for example, sufficient which is less than the radius of the exhaust pipe.
The guide baffle according to the invention is composed essentially of web plates of essentially radial orientation as well as one or more peripheral sheets to which the web plates are connected at their ends facing the tube wall; the peripheral sheets in turn are fitted to the tube wall, e.g. by welding or press-fitting into the exhaust pipe. The seating of the guide baffle in the exhaust pipe may be secured by interlocking the exhaust pipe with the peripheral sheet of the guide baffle, e.g. by the pressing of catches into the exhaust pipe, which interengage with matching catches of the peripheral sheets.
The web plates of the guide baffle are so designed that they extend essentially radially or essentially rectilinearly when viewed through the exhaust pipe in cross-section. The web plates may be provided in optional even numbers; however, an uneven number may also be found advantageous, e.g. in the form of three web plates in a Y-pattern. In practice, a guide baffle in the form of a pinched xe2x80x9c8xe2x80x9d, and thus comprising four radially extending web plates and two peripheral sheets connected there between was found to be advantageous.
Due to the fact that the transitional region between peripheral sheets and web plates in the aforesaid embodiment defines a radius, the trend of the web plates not to interengage is further increased since the radius increases with rising temperature in the sense of a leveling of the bend, whereby the web plates are drawn apart. Possible thermal stresses and resulting crack formations are counteracted due to the web plates not being in contact with one another, i.e. the life expectancy of the guide baffle corresponds to that of the entire exhaust train.
The guide baffle according to the invention is preferably fitted directly to the outlet of the exhaust turbocharger, preferably so close thereto that the guide baffle is closer to the outlet cross-section of the turbocharger than corresponds to the axial length of the web plates.
The guide baffle according to the invention may also be fitted at locations of the exhaust pipe of a motor vehicle or of an internal combustion engine other than between the exhaust turbocharger and the inlet of the catalyst, i.e. wherever a flow stabilization may be necessary. However, it was found in practice that contrary to conventional theories of aerodynamics the afore explained small length of the guide baffle in the direction of flow is adequate.
In the following an embodiment of the device according to the invention will be further explained with reference to the drawing. There is shown in